One of the problems associated with solar ovens is that their construction does not afford frequent use over an extended period of time. Furthermore, designs are not capable of maintaining high, constant cooking temperatures.
A great number of prior art solar ovens, because of their lack of weight and size, are considered "portable," while fewer solar ovens are considered "nonportable." An example of a nonportable solar oven is disclosed in U.S. Pat. No. 4,655,196, by Kerr. The Kerr solar oven is adapted to be permanently installed in an exterior wall of a building. The Kerr oven has an access door system which opens through the exterior building wall into the kitchen. A plurality of reflective panels direct sunlight through a glass front wall into the oven. The oven also includes a heat absorbing element onto which cooking vessels may be placed for cooking food. Another example of a nonportable solar cooker is disclosed in U.S. Pat. No. 4,696,285, by Zwach.
Among the many disadvantages of existing portable solar ovens currently available are the materials of which they are constructed and the construction techniques used to assemble those materials. One such portable oven is manufactured by Kerr-Cole of Tempe, Arizona. The Kerr-Cole solar oven includes materials such as corrugated cardboard, foil, glass, wood moldings, contact paper, and crumpled newspaper insulation. As can be readily surmised, exposure of the Kerr-Cole solar oven to such adverse elements as rain or wind results in the Kerr-Cole oven having diminished structural integrity.
Another portable solar oven is manufactured by the Burns-Milwaukee Corporation of Milwaukee, Wisconsin. The Burns-Milwaukee solar oven includes a vinyl exterior case having a black metal box disposed therein. Fiberglass insulation is placed between the metal box and the exterior case.
The Burns-Milwaukee case is covered with a single hinged pane of glass. A four-sided polished aluminum reflector is attached to the outer periphery of the solar oven to increase the amount of sunlight entering the interior of the metal box. A swinging shelf is in the interior of the metal box upon which food may be placed.
In use, the box is tipped forward and secured in any one of ten positions. These positions are indicated by ridges molded into the exterior case. The various positions are promoted for allowing sun exposure to the interior of the metal box.
One disadvantage of the Burns-Milwaukee solar oven is that it is light, and wind against the exterior of the case may cause jarring of the oven and result in a cooking vessel's contents spilling. A further disadvantage is that the lack of weight and loose attachment of the four-sided polished reflector allows it to be blown from the solar oven by a light breeze. This may result in damage, and cause jarring of the oven. This jarring may result in the spilling of a cooking vessel's contents inside the box. Additionally, with the use of the foursided reflector, the oven's position must be adjusted regularly to face the sun so that the reflector does not block the sunlight from the interior of the metal box.
A disadvantage of these ovens is that food is placed in the oven through the top. When accessing the inner portion of the oven through the top, a heat loss of at least 25.degree. F. is unavoidable. Thus, as food is cooking and repeatedly being checked for "doneness," the time necessary to cook food in the oven is increased, since the average temperature is greatly diminished. The Burns-Milwaukee solar oven has a maximum achievable temperature of 375.degree. F. in warm summer months, with a maximum average temperature of 290.degree. F. to 300.degree. F., for no more than one and one-half hours on clear days. The Kerr-Cole solar oven has a maximum achievable temperature of 250.degree. F. in summer months.